Last May I added a D610 to my bag.
I don't say upgrade as I kept my D5100 and it does see occasional use - mostly in my wife's hands now. She is starting to get the hang of the DSLR and I'm hoping she'll get more into it, right now she is very happy 'auto-everything' but she just loves the photo's she is getting with our 35mm DX lens.
But I wanted more and dove into the deep end of the D7100 vs D610 debate. Watched lots of Youtube reviews and read many an on-line recommendation. Handled both of them at camera shops and discussed it (way too much according to my dearly beloved). Eventually it came down to looking at both of them in the shop and my wife asking me if I'd feel like I 'settled' for the D7100 when I really wanted the D610. That did it and I bought the D610. It was my 60th birthday and my darling put a 60mm F/2.8 on the counter "a 60mm for your 60th birthday". Very sweet. I did not get the kit lens.
Since then I've begun my quest for FX lenses. Yes I did try the DX lenses and they do work. But you will want FX lenses. I happened to have two old lenses from a F60 film Nikon from about 2000. They work just fine. I've only bought one other new lens - a 50mm 1.8 AF-D (bargain clearance at a store closing it's doors). All the rest are older, vintage, legacy (or just call them cheaper) used lenses from stores, private sale and eBay. I keep MS Windows Shopping on my PC looking at Kijiji, eBay and the on-line offerings of various venders of used lenses. Want more solid F 2.8's. Looking hard at a 24mm F2.8 AF-D prime lately, and would love a 70-200 (or 80-200) F2.8. And eventually a long lens to 600mm but I've over spent my fun money budget for a while. Point is, if you shop around and if you are open to older lenses you can build up a very usable collection - and then someday trade them in for a newer lens when you can afford it.
These older lenses are probably not going to depreciate any more and if kept properly will be desirable trade ins. The new DSLR's are giving these old lenses a new lease on life. My D610 is good with higher ISO values meaning you can crank the ISO on lenses that do not have modern V.R. to compensate - this will improve shutter speed for a given F stop for very little reduction in noise quality - which can often be cleaned up in pp with the right software - although that is usually not that necessary. I'm not talking 6400 - you just need to go to 1600 or 2000 to get an acceptable shutter speed to work at the F stop you want to use.
Unless of course money is no object for you in which case just buy a D810 and all the lenses you want new.